The present proposal deals with a series of investigations aimed at clarifying the mechanisms of oncogenic transformation by avian sarcoma viruses (ASV). The main effort will be to further characterize genetically and biologically two new ASV's, UR1 and UR2, recently described by us. We plan to isolate conditional (ts) and nonconditional partial deletion (ptd) mutants in order to obtain a physical/genetic map of the gene ros, the unique sequence of isolate UR2. We will also attempt to dissect this gene by correlating the sites of selected ts mutation with the phenotypic expression of transformation parameters. These transformation parameters will also be investigated for wild type UR1 and UR2. A detailed study of the mitogenic activity of these viruses for neuroretinal cells is also a goal of the biological characterization of UR1 and UR2. We plan to investigate the intracellular location of the protein products of UR1 and UR2 by immunofluorescent and fractionation studies of transformed nonproducing cells. The interaction of these proteins with cytoskeletal components will be investigated. We will finally attempt to identify the protein product of c-ros, the cellular gene homologous to the specific sequence of UR1 with the hope to elucidate the function of this gene in normal cells. These studies hopefully will contribute to the understanding of avian transforming genes and their mechanism(s) of oncogenic transformation.